A tetrafluoroethylene/propylene copolymer (hereinafter sometimes referred to as a “TFE/P copolymer”) is used for hoses, tubes, gaskets, packing, diaphragms, sheets, electric wire covering materials, etc., as an elastomer material which is excellent in properties such as heat resistance, oil resistance, chemical resistance, electrical insulation properties, flexibility, etc. and which is radiation cross-linkable.
Further, in order to supplement the properties of a TFE/P copolymer, it has been proposed to blend an ethylene/tetrafluoroethylene copolymer (hereinafter sometimes referred to as “ETFE”) to the TFE/P copolymer.
For example, in Patent Document 1, it is attempted to improve mechanical properties such as tensile strength and tear strength, or properties such as toughness, etc. by blending ETFE to a TFE/P copolymer. And, in Patent Document 1, for the purpose of lowering the compound price, a large amount of an ethylene/acrylate copolymer or an ethylene/vinyl acetate copolymer is further blended in addition to the TFE/P copolymer and ETFE.
In Patent Document 2, in order to improve the cut-through properties (properties less susceptible to thermal softening at high temperatures) of a TFE/P copolymer, ETFE is blended together with calcium carbonate.
Also in Patent Document 3, in order to improve the cut-through resistance, ETFE is blended. Patent Document 3 discloses that if the ETFE to be blended to a TFE/P copolymer is too much, the flexibility and elongation tend to decrease, and therefore, the blend ratio of ETFE to the entire blend polymer should be at most 40 mass %.
Further, for applications for which a high level of flame retardance is required, a flame retardant is incorporated in a TFE/P copolymer.
For example, in the above Patent Document 3, from 0.5 to 20 parts by mass of antimony trioxide as a flame retardant is incorporated per 100 parts by mass of the blend polymer.